There exists a wide range of devices that depend upon the transmission of signals to monitor or measure various biological or environmental parameters of a patient. For example, various forms of blood oximetry devices employ the transmission and reception of signals in the measurement of one or more biological or environmental parameters of a patient.
Blood oximetry devices are commonly used to monitor or measure the oxygen saturation levels of blood in a body organ or tissues, including blood vessels, or the oxidative metabolism of tissues or organ. These devices are also often capable of and are used to determine pulse rate and volume of blood flow in organs or tissues, or to monitor or measure other biological or environmental parameters.
As is well known to those of skill in the arts, blood oximetry devices measure the levels of the components of one or more signals of one of more frequencies as transmitted through or reflected from tissue or an organ to determine one or more biological or environmental parameters, such as blood oxygenation level and blood volume or pulse rate of a patient.
Blood oximetry devices may also be constructed as directly connected devices, that is, devices that are directly connected to a patient and that directly present the desired information or directly record the information and as remote devices, that is, devices attached to a patient and transmitting the measurements to a remote display, monitoring or data collection device.
Blood oximetry devices measure blood oxygen levels, pulse rate and volume of blood flow by emitting radiation in a frequency range, such as the red or near infrared range, wherein the transmission of the radiation through or reflectance of the radiation from the tissues or organ is measurably affected by the oxygen saturation levels and volume of the blood in the tissues or organ. A measurement of the signal level transmitted through a tissue or organ or reflected from a tissue or organ may then provide a measurement or indication of the oxygen saturation level in the tissue or organ. The transmitted or reflected signals may be of different frequencies which are typically affected in measurably different ways or amounts by various parameters or factors or components of the blood.
Parameters represented by transmitted or reflected signals may be represented by different and related or unrelated parameters of the received signals. For example, a signal transmitted through or reflected from tissue or an organ to measure, for example, blood oxygenation or flow, may have a constant or “dc” component due to the steady state volume of blood in the tissue or organ and a time varying or “ac” component indicative of the time varying volume of blood flowing through the tissue or organ due to the heart beat of the body. Each signal component may provide different information, and may provide information that may be used together to generate or determine yet other information.
Recent developments in medical devices, and in particular in medical monitoring and data collection or monitoring devices, such as blood oximeters, has been in the direction of smaller, lighter and more portable devices. Such “miniaturized” devices may be used, for example, for remote or portable use, such as by EMTs, or as individual user device. The development of such smaller and more portable devices, however, has meant greater reliance on smaller, more portable or more convenient power sources to drive the devices, such as batteries as opposed to connections to power lines. This trend has led to greater concerns regarding power consumption and battery life of the devices. For example, in a typical blood oximetry device or system, up to 75% or more of the power consumption of the device is used in driving the light sources, for example light emitting diodes (LEDs) or vertical-cavity surface-emitting lasers (VSCELs), generating the red or infrared signals that are transmitted through or reflected from the tissue or organ to measure the levels of oxygen in the tissue or organ.